Optimizing squeezing in a coherent quantum feedback network of optical parametric oscillators

TL;DR

This paper demonstrates how a network of two coupled optical parametric oscillators, optimized using global algorithms, can significantly enhance and tailor the squeezing spectrum of output light compared to a single OPO, with robustness to phase variations.

Contribution

It introduces an optimization framework for CQFC networks of coupled OPOs to maximize squeezing performance across spectral ranges, outperforming single OPO systems.

Findings

Optimized CQFC network achieves higher squeezing than single OPO.

Global search algorithms are essential for optimal performance.

The squeezing performance is robust to small phase variations.

Abstract

Advances in the emerging field of coherent quantum feedback control (CQFC) have led to the development of new capabilities in the areas of quantum control and quantum engineering, with a particular impact on the theory and applications of quantum optical networks. We consider a CQFC network consisting of two coupled optical parametric oscillators (OPOs) and study the squeezing spectrum of its output field. The performance of this network as a squeezed-light source with desired spectral characteristics is optimized by searching over the space of model parameters with experimentally motivated bounds. We use the QNET package to model the network's dynamics and the PyGMO package of global optimization algorithms to maximize the degree of squeezing at a selected sideband frequency or the average degree of squeezing over a selected bandwidth. The use of global search methods is critical for identifying the best possible performance of the CQFC network, especially for squeezing at higher-frequency sidebands and higher bandwidths. The results demonstrate that the CQFC network of two coupled OPOs makes it possible to vary the squeezing spectrum, effectively utilize the available pump power, and overall significantly outperform a single OPO. Additionally, the Hessian eigenvalue analysis shows that the squeezing generation performance of the optimally operated CQFC network is robust to small variations of phase parameters.